1. Field of the Invention
It is object of this invention to provide an axial propeller, whose blades are not twisted and are equipped, in coincidence with the trailing edge, with tabs having suitable dimensions and orientation, particularly in the blade zones with lower peripheral speed.
In this way an advantageous increase of the effective displacement of air of an axial propeller whose blades are not twisted, can be obtained, in particular at the blade zones with lower peripheral speed.
2. Description of the Prior Art
At present the increase of the effective displacement of air at the blade zones with lower peripheral speed is achieved by means of one of the following methods:
(a) Increase of the blade's chord (width) proceeding from the external end to the blade's root PA0 (b) Blade's twist (=increase of the geometrical incidence angle of the blade's sections, proceding from the external end to the blade's root) PA0 (c) Combination of the methods mentioned in (a) and (b). PA0 (1) The chord change of the blade's profile is not feasible on massive blades, manufactured by extrusion, and is complex with hollow blades particularly if reinforced. PA0 (2) The twist of blades made of plastic material and obtained by extrusion is not feasible. PA0 (3) The twist of blades made of light alloy and obtained by extrusion, shows the following inconveniences:
Such techniques, which are used at present, exhibit the following inconveniences:
necessity to exceed the yield point of the material; PA1 practical impossibility to reach suitable twist values (particularly on blades having shell section and low elongation ratio, defined as the ratio of the blade's length to the chord) without causing damage to the blade itself.